FIG. 1 is a networking diagram of a single network of an NGN. As shown in FIG. 1, the media gateway controller (MGC) and the media gateway (MG) are two key components of the NGN. The MGC is responsible for the call control function, and the MG is responsible for the service bearer function so as to separate the call control plane from the service bearer plane. Thus the network resources can be shared fully, equipment upgrade processes and service extensions may be simplified, and development and maintenance costs may be reduced greatly. Under the control of the MGC, a Real-time Transfer Protocol (RTP) media stream is established for communication between different MGs.
A control protocol needs to be applied between the MGC and the MG for interworking between them. The media gateway control protocol is a main protocol for communication between the MG and the MGC. The currently prevalent protocols are H.248/MeGaCo Protocol and Media Gateway Control Protocol (MGCP).
Taking the H.248 Protocol as an example, various resources on the MG are abstractly represented by terminations. Terminations are categorized into physical terminations and ephemeral terminations. Physical terminations are physical entities which exist semi-permanently, for example, time division multiplex (TDM) paths. Ephemeral terminations refer to the public resources which are requested for an ephemeral purpose and will be released after being used, for example, RTP streams. Specially, a root termination refers to the whole MG. The combinations between terminations are abstractly represented by contexts. Because a context may include multiple terminations, a topology is used to describe the interrelations between terminations.
Based on the abstract model of MGCP, a call connection is actually an operation on the termination and the context. Such operations are performed through Commands, Requests, and Replies between the MGC and the MG. Commands include Add, Modify, Subtract, Move, AuditValue, AuditCapabilities, Notify, ServiceChange and etc. Parameters of Commands, also known as descriptors, are categorized into property, signal, event, and statistic categories. The parameters with service relevance are logically aggregated into a package.
Under the control of an MGC, the MG is responsible for converting and transferring media streams between a user and a PS network and between PS networks in different IP domains. FIG. 2 is a networking diagram for IP cross-domain interworking in an NGN. As shown in FIG. 2, the system includes two network domains: IPa and IPb. MGCa are media gateway controllers in the IPa network domain, and MGCb are media gateway controllers in the IPb network domain. MGCa and MGCb are designed to control the MG of the IPa network domain and the MG of the IPb network domain, respectively. MGia and MGib are edge MGs designed to implement communication between MGs of adjacent network domains. The MGa can perform media conversion and transfer between a Plain Old Telephone Service (POTS) user and an RTP media stream. The MGb can perform media conversion and transfer between a TDM trunk and an RTP media stream. The MGia and MGib can perform media conversion and transfer between RTP media streams.
To ensure the quality of service (QoS) and communication security, the MGC should perform packet filtering for the media streams transferred (e.g., received and transmitted) by the MG, i.e., permitting or forbidding the media streams of certain characteristics to be input or output through the MG.
Currently, in an IPv4-based PS network, a media stream can be uniquely identified by the basic characteristics of a quintuplet (e.g., source address, source port, destination address, destination port, and protocol type) thus filtering the packets for a specific media stream by the elements in the quintuplet. However, all elements in the quintuplet are not available from the IP packet header and some elements such as source port or destination port need to be obtained by resolving the IP packet body. The IP packet body involves upper-layer protocols or segments or involves other factors such as encryption so the resolution is difficult and the packet filtering is more complex.